Impossible
by prodigaldaughter13
Summary: "Cas. I can't- I can't let you give up everything you are, for us. If you lose your grace… You'll lose yourself. It's not like Sam or me dying. We'd still be us, in our heavens. But you don't know who you'll become if you Fall."
1. Chapter 1

Impossible. Freaking impossible.

"No way in hell is that happening," Dean insisted. Kevin and Sam both gave him a stern look, while Cas only seemed grimly accepting. Dean persisted though. "No. I- _We_," he corrected quickly, "Just got you back, man. No way are we letting you pull some sacrificial bullshit."

Sam opened his mouth to reply, but Cas held up his hand to stop him. "I believe it would be best if I spoke to Dean about this alone," he said softly, inclining his head towards Kevin and Sam significantly.

The boys both nodded, and they left the room. They'd been in the library of the bunker, but now Castiel craved a slightly more… comfortable setting in which to have this painful discussion. Without awaiting Dean's permission, he transported them both back to Dean's room, the only place in the bunker Castiel felt completely at ease.

Instead of complaining about the unwanted mojoing, Dean just sat down on the edge of the bed. "Cas, man, you aren't doing this."

Castiel pulled the chair from the corner –his chair, the chair Dean had left out for him, in the hopes of his return– and sat facing his hunter with a sense of serious determination.

"Dean," he began, "You and Sam are too valuable to be lost. I am, in the grand scheme, unimportant. And it is not as if I will cease to exist. I will Fall, but I do not believe it will destroy me." Cas sat back, hoping Dean would see reason.

But his hunter leaned closer, green eyes drowning in some sort of knowledge, and took the angel's hands in his own.

"Cas. I can't- I can't let you give up everything you are, for us. If you lose your grace… You'll lose yourself. It's not like Sam or me dying. We'd still be us, in our heavens. But you don't know who you'll become if you Fall." Dean shifted uncomfortably, flashing back to the future Zachariah had shown him. He never wanted to see Cas's eyes go dead like they had been, never wanted his angel brought so low that only drugs could numb the pain. He couldn't let it happen.

"What I know," Cas argued, "is that I cannot see you die, nor can I watch you suffer if Sam were to make the sacrifice. It is best I risk myself; you will lose nothing." He said it like it was the most obvious thing in the world, and not the complete opposite of truth. Dean scowled, gripping the angel's hands tighter.

"I would lose you," Dean said, eyes blazing now, anger and pain bubbling under his skin.

"As I said." Cas's voice was hollow now, his eyes going dull, too similar to the future Cas Dean had seen. "Nothing."

That last word, the affirmation that Cas had already lost so much of himself, broke something in Dean, making him release the angel's hands and instead grab him by the shoulders, crashing their lips together fiercely.

"Everything," Dean huffed when he pulled back a moment later, settling onto the edge of the bed once more. His brain finally caught up with his instincts, and terror settled into his bones. He'd crossed a line, he knew it, and if Cas's stunned gave was anything to go by, it was one hell of a line he'd blown past. He opened his mouth, an apology already on the tip of his tongue, when he found himself suddenly knocked back onto the mattress, Cas's lips pressing against his once more.

For the first time since Purgatory, Dean felt… happy. No, that wasn't the right word. _Ecstatic._ There was an edge of desperation to it, the fear that Cas might still go through with the plan to close Hell off, but most of it was buried under the wash of _Cas_ that was covering every plane of his body and mind. After a moment of just savoring the feeling of Cas's slightly chapped lips on his, Dean parted his lips, encouraging Cas to do the same.

Dean had figured if this ever happened, he'd be the one running the show, but the moment Cas opened his mouth, Dean knew he was in for a ride. Then again, if it was his angel leading, there wasn't a place in the world Dean wouldn't follow.

Castiel threaded his fingers through Dean's hair, marveling that he was allowed to have this, that Dean was willing to give this to him in spite of his mistakes and the pain he had caused his hunter. Dean pulled back, just a little, and Castiel let him go only so he could catch his breath.

After a moment of hushed silence, punctuated only by their heaving breaths, Dean spoke. "Just… just don't do anything unless you're sure, okay?" he asked, and if Castiel didn't know better, he'd swear Dean was begging. He realized belatedly that Dean's hands were gripping his hips like they were a lifeline, holding their bodies close together.

The angel looked down at Dean, studying his face carefully. He seemed almost frightened; there was a protective sort of light in those green eyes that Castiel usually only saw aimed at Sam. Castiel leaned down, pressing his lips gently to Dean's brow, wanting to smooth away the lines of worry furrowing there.

"I'm already certain, Dean. I will not lose Sam, and I cannot lose you," Castiel said lowly, his voice rough with more emotion than he was used to expressing to Dean. "You have both sacrificed so much."

Dean sat up suddenly, holding onto Cas to keep him in his lap. "And you haven't? Castiel, you've given up everything for us, for me. And now you want to give up the last of what you have?" Dean shook his head and tightened his arms around the angel. "I can't ask you do to that."

"You aren't asking. I'm giving," Castiel whispered, leaning down so his forehead rested against Dean's. They sat like that for a time, Cas with his legs wrapped around Dean's waist and Dean holding tightly to Cas's waist, afraid if he let up on his grip the angel would mojo out and go on with the plan without him.

Castiel leaned forward, pressing a tentative kiss to Dean's lips, and when Dean sighed appreciatively, he deepened the kiss, slipping his tongue into Dean's mouth to taste him. Dean shuddered beneath him, finally joining in fully, pressing up towards Castiel urgently.

Without really thinking, Dean pushed Cas's trench coat off, loving the thump it made as it hit the mattress. He was working on tugging the tie off when he heard the door bang open.

"So get thi- Jeez, guys! Sock on the door next time!" Sam exclaimed, holding a book in one hand and a horrified expression on his face. Not oh-my-God-my-brother-likes-dudes face (they'd had that talk _ages_ ago) but very much an oh-my-God-my-brother-is-banging-an-angel face.

"My bad, Samantha, I forgot you don't knock," Dean teased easily, holding Cas in place when he went to move off Dean's lap.

"No, but really, Kevin's got some important stuff to tell us, so you gotta come to the library. And… it's about damn time, you two. So. Good job." Sam turned to leave, but then twisted back. "Cas… put on your coat. You look naked without it." And he left, leaving the door open behind him.

Dean grinned up at Castiel, stretching a bit to kiss him chastely before grinning broadly. Castiel raised an eyebrow, but slid neatly off Dean's lap before standing and pulling his coat on. He managed to make it halfway across the room before Dean caught him and pulled them together, kissing him sweetly one more time before releasing him completely, except for the fierce hold he kept on the angel's hand. Dean didn't let go, not even when they reached the library, where Sam and Kevin both sat at the table, pouring over books of lore.

Sam looked up as the pair walked in. "Hey, Romeo," he greeted casually.

"Shut your cakehole, Samantha," Dean replied easily, sprawling out in the chair next to his brother as Cas settled in next to him. "So, Moses, what you got for us?"

While Sam grinned, Castiel noted that Kevin looked particularly serious. A tinge on unease settled in Castiel's stomach, and it must have shown in his face because Dean gave his hand a reassuring squeeze.

"You aren't going to like this," Kevin warned. Dean gave a snort –because really, when have they _ever_ liked what the prophet told them– but Cas gave him a look that silenced him while the prophet spoke. "Basically, there are only a few days you _can_ close Hell; the spring and fall equinoxes."

"And those happen when?" Dean asked, already getting a sinking feeling in his stomach.

Kevin confirmed the feeling with his answer. "Tomorrow."

Castiel nodded. "So that means…" He didn't even want to finish the sentence. Just because he'd made his decision didn't mean he was completely confident saying it. Especially when it seemed to bother Dean so much.

"Tonight's your last night with grace."


	2. Chapter 2

Dean's face had fallen the moment he realized how soon Cas would be giving everything up. Sam and Kevin were talking back and forth with Cas, making plans for the next day and the ritual they would have to perform, but it all went over Dean's head. All he could think about was what Cas was giving up, what Cas was sacrificing, for _him_, some speck of a human who had been nothing but trouble for the angel from the start.

When Dean started to frown in earnest, Castiel made his excuses to Kevin and Sam and pulled Dean along with him out of the library. Dean trailed half-heartedly behind Castiel, keeping up only because Castiel wouldn't release his hand. An eternity later, they made it to Dean's room, and the moment they were inside, Castiel whirled and pinned Dean to the closed door. Without a word he crushed their lips together, not giving him time to think about what would happen the next day, or anything else beyond this moment together.

Reacting on instinct, Dean arched up against Cas, pushing the trench coat to the floor –and wasn't _that_ a satisfying sound– and pressing closer until Cas's legs go weak and they're both leaning against the wall, still kissing furiously. Cas doesn't do the gentle approach, and Dean is just fine with that. He can take it, and enjoys the little nips and tugs Cas gives his bottom lip now and then, making Dean gasp into his mouth before Cas comes back up to delve in and take until they're both quivering messes.

Dean's hands find Cas's waist, and make quick work of his belt and shirttails, untucking them and tossing the belt to the side with a loud _thunk_before realizing he'd have to get the tie off Cas before more progress can be made stripping him.

By the time Dean gets his tie off, Castiel has peeled away the outer layer of plaid and is hiking Dean's tee shirt up quickly, eager to touch every inch of warm skin, feeling all the places he'd joined the man together and all the scars he'd gained since. The tee is pulled right off and discarded as Dean pushes against Castiel's chest and moves them away from the door.

They separate for a moment, and in that time Dean is able to realize exactly where this is going. And he is able to worry.

"But, dude… if we do this… won't you Fall?" Dean asked, thinking back to Anna, then immediately feeling guilty. He couldn't do something like that to Cas. Not because they needed his grace, but because _Cas_ didn't deserve to Fall. Not after all he'd been through.

"Falling isn't about sin, Dean. It's about desire," Castiel said, blinking slowly in that odd way of his, like he couldn't quite pinpoint something about Dean.

Dean frowned a bit. "Oh. So you don't… desire me." So this was a fling, something to get out of his system before he lost his grace. Dean tried not to let his hurt show in his voice, but judging by the sudden concern in Cas's eyes, he'd failed.

Cas moved closer than ever, an impressive feat, considering how close they already were. "Dean. That- that isn't what I meant at all. It is the desire_to fall_ that makes an angel fall, not the sin. The sin is… symbolic. Necessary, but not damning on its own." The angel took another small step towards him, so close now that Dean's eyes crossed trying to focus on those blue eyes. "I do desire you. Very much." Cas was frank, always had been, and now Dean was thankful for it.

"Good, good," Dean repeated, nodding a bit. "Because ah- I um desire you too. A lot." Okay, so maybe his game was a little rusty, but hey, at least he tried. And his point had been made clear.

Something close to a smirk paints Cas's face, and the angel's hand drifts lower to palm lightly at Dean's crotch, where he's already half-hard from their make out session against the door. "I had realized that," Cas said lowly, leaning in to whisper against Dean's ear. Dean shuddered, his hands coming up of their own volition to wrap around Cas's jaw and bring his lips up for Dean to taste. Cas made an impatient sound and took control of the kiss, moving so that he could press Dean over and down onto the mattress. When Dean was situated in the center of the bed, he straddled the hunter and leaned down to speak in his ear.

"I am going to take you apart at the seams, Dean Winchester, and then I am going to put you back together so that every part of you bears my signature," he growled, and loved how Dean shivered beneath him. While he was still close to Dean's ear, he took the earlobe between his teeth, laving at it with his tongue before nipping it roughly, drawing a half-moan from Dean's mouth. His hand automatically slid over the handprint on Dean's shoulder, and electricity danced between them the moment contact was made.

Dean was starting to lose his mind, pushing his hips up against Cas, trying desperately to get some friction on his cock, but Cas was having none of it, instead the angel teased with clever teeth and tongue, tracing nonsense patterns down Dean's neck and torso, nipping a the ribs and navel as he passed them and then –good Lord– undoing the button on Dean's jeans with his _teeth_ and then catching the zipper and tugging it down with his_fucking teeth_, warm breath ghosting over Dean's cock, so close to being free but still separated by a thin layer of boxers.

Castiel slowly pulled the jeans off of Dean, relishing in each inch of exposed skin as the denim revealed it. He gave a small quirk of his mouth when Dean moaned and tugged at Castiel's slacks, trying to remove them as quickly as possible while still maintaining physical contact. Castiel, just as eager to touch Dean as Dean is to touch him, impatiently wiggled out of his trousers and underwear in one go, his cock bobbing up, already slick with precome that smears slightly on his stomach as he leaned down to remove Dean's boxers with a sharp yank. He then pressed close until their cocks were rubbing together beautifully and his mouth was tracing silent words and promises across Dean's neck and chest.

Eagerly, Dean fumbled with one hand towards the nightstand, finally finding the lube –not bad considering he was doing it while Cas's tongue was doing absolutely _sinful_ things to his neck– and slipped the tube into Cas's hands. At the angel's confusion, Dean managed to gasp out an explanation. "Please, Castiel… Want you to… fuck me."

Cas stared down at him for a moment, like he was trying to make sure Dean was serious, then gave a nod and poured some of the lube into his hand, warming it slightly before tracing one finger across Dean's hipbones, making the hunter gasp at the sudden change in sensation as the lubed finger traced over his balls and down further, dragging slowly across his perineum until it circled his entrance.

Without warning, Castiel plunged the tip of his finger into Dean, loving the way the hunter clenched around him, then relaxed as the discomfort gave way to pleasure. Just as promised, Dean was falling apart, canting his hips up as Castiel rolled them onto their sides to give him better access to Dean's hole. Soon his entire finger was disappearing into Dean, stretching him out until he was ready to take two.

Once the two were in, Castiel was able to seek out the spot in his body that made Dean keen out with surprised pleasure. He purposefully hit it at random, keeping Dean on edge as he added in a third finger, ensuring that Dean would feel as little pain as possible when Castiel finally breached him.

When Cas completely withdrew his fingers, Dean let out a whimper, lifting his body in submission, trying to get Cas to fill him up again. He was shameless about what he wanted; if Cas didn't fuck him into the mattress in the next five minutes, he was pretty certain he was going to die. Cas started pushing Dean's knees up towards his chest, and when Dean went to roll over, Cas stopped him.

"No. I want to see your face when you fall apart." And _Christ_ who would've guessed the thousand-year-old virgin's version dirty talk would nearly be enough to make Dean come before they really got started?

And then the head of Cas's cock was pressing into Dean, and Dean completely lost whatever semblance of control he'd managed to maintain through the foreplay. By the time Cas was in to the hilt, Dean was writhing and moaning against the sheets, his hands gripping Cas's shoulders like he was about to explode.

Castiel should have been embarrassed at the sounds he was making, the pleas and cries that were bursting out of him as he slammed in and out of Dean, hitting the man's prostate on each thrust. He could feel his orgasm approaching, but he was determined to see Dean come first.

He slipped his hand down and fisted Dean's cock, pumping once, twice, three times before Dean falls apart, a scream of "_Castiel_," exploding out of him as he spilled his release across Castiel's fist.

"C'mon, Cas," Dean gasped, coming down from his high. "Come for me, angel."

And at the sound of his hunter, his _Dean_, begging, Castiel flew over the edge, spilling his seed deep inside Dean before going completely boneless and pulling out gently. He lay back on the bed, one arm wrapped gingerly around Dean, resisting the urge to pull the man to him and hold him tightly to his chest. He was uncertain how the desire to cuddle would go over with Dean.

Dean moved closer, curling up against Cas's chest and resting his head over where Cas's heart was hammering away, but slowly starting to settle.

"We're gonna stick together like this, you know," Dean commented, gesturing to their chests, both coated in Dean's come. Cas only smiled, and mojo'd the mess away, even managing to clean what was dribbling between Dean's thighs.

The hunter grinned. "Awesome."


	3. Chapter 3

The next day, Sam and Kevin took a Kevin's car, letting Dean and Cas drive in the Impala to the warehouse they'd picked to perform the ceremony in. Dean held on to Cas's hand the entire way, looking over at his angel with worried eyes as often as he could. When Cas would catch him looking, he'd give the angel's hand a squeeze and smile.

Yet Castiel still knew Dean was worried. He suspected there was more to his worry than what dean was letting on, but as Dean didn't seem ready to share it, Castiel wasn't going to push the issue. Instead he sat quietly, enjoying the last hour or so of his grace. He spent most of the drive staring at Dean; at the soul Castiel could see shining out of him. No matter where Dean was, his soul was brilliant, the most shining thing Castiel had ever seen. If he was being truly honest, it was the only thing he would honestly miss and long for once his grace was gone.

But there were other ways to see Dean's soul. In his eyes, his smile, the way he said Castiel's name, as if it was the only prayer he'd ever need. The careful way he drove, fast but not out of control, the way he felt at three o'clock in the morning, having woken from a dream only to curve infinitely closer to Castiel.

The ride was over far too soon; they pulled up only moments after Sam and Kevin. The four paused outside the warehouse, hushed by the significance of what they were about to do. Castiel was the first to step into the warehouse.

"Hang on, guys," Dean said when Kevin and Sam made to follow him. "Let's give him a minute."

Castiel slipped inside, using his grace to arrange the area to the specifications of Kevin's revelation. A makeshift altar of sorts was built, and the area around it cleared of the dust and grime of the years. Once everything but incantations were in place, Castiel took a moment to himself.

He knelt before the altar, head bowed, knowing this was his last moments as an angel, and wanting to speak to his father one last time before things changed.

"Father. There are many of my brothers and sisters who would say that what I am doing is wrong. I believe, more firmly even than I believe in you, that they are wrong. You gave us each the power to choose, and you asked us to love these humans more than we loved even you. I may not be able to follow that for all humans, but I have found some that I love. And one that I will give everything for. I will not make the same mistake Lucifer made, and place loving you above doing what I know is right. This, here, with the Winchesters, this is right. This is my faith, and this is my choice. It is, as it always will be, with them. This is what I was created for. Thank you for this purpose I never thought to ask for. Thank you for my grace, and for enabling me to make this sacrifice. Thank you for him." With those final words, Castiel rose and turned around, only to see Dean waiting patiently, just out of earshot, for him to be ready.

"Where are Sam and Kevin?" Castiel asked, stepping towards Dean, giving him permission to come closer. Dean did, stepping until they were only a few inches apart.

"Kevin said that if anyone had the authority to do this, it was me. He told me what I needed to say, how we needed to do this. If you're okay with it, it's just you and me," Dean said solemnly, none of his usual sarcasm leaking into the words. He knew this was serious, possibly the most serious thing he'd ever done, and he didn't want to fuck this up by doing or saying the wrong thing.

Cas gave a small smile, the twinkling kind that made Dean's heart speed up. "I think I would like that very much," he said with a nod.

"Okay. You might wanna get comfortable first, this could be a little long," Dean suggested, and he helpfully took Cas's trench coat and suit jacket when they were offered. "Here, hop up on this and lie down," Dean said, patting the altar and trying not to think of Cas as a sacrificial lamb. While Cas got comfortable, Dean circled the altar, painting symbols on the floor identical to the drawings Kevin had prepared for him.

He'd never tell Cas, but as he worked painting the sigils across the floor, he sent up a silent prayer to whatever God happened to be listening.

_I know I don't do this much –I'm more likely to believe in Cas than you– but just… let him be okay. Let Zachariah be wrong. Let this work, and even if it doesn't, let Castiel be okay._

He straightened up, finished with the sigils, and stepped to the altar to look at Cas. "You ready?" Dean asked, wanting to give Cas one more chance to back out. Cas nodded.

"I am ready, Dean."

"Okay." Dean took a shaky breath, and leaned down to press a soft kiss to Cas's forehead, stubbornly refusing to think of this as a goodbye. Kevin had said there was a _chance_ Cas would be destroyed, but that it was slim. So they were fine. Completely fine. Dean took another breath, and started to recite.

"Domine, suscipe spiritum gratiæ, et sacrificium, et dilectione, in castitate. Hostias Hostias et ambulare super terram praesidia sponte inferiores, qui pugnabant desuper et fallere volunt." _O Lord, accept this sacrifice of grace and spirit, given in purity and love. Allow this sacrifice to protect those who freely walk upon the earth from those who fought from below and who seek to deceive._  
The words sounded around the couple, echoing oddly in not only Latin, but in English, and Arabic, and Hebrew, and a thousand other languages Dean couldn't begin to identify. He looked down at the angel, to see how he was doing, and gasped.

Castiel's wings had manifested fully, not simply the shadows, but the full out, twelve-foot wings. Massive wings, the deep blue-black of a starless night sky, spread over the side of the altar until they trailed on the floor.

"Dean! Close your eyes!" Castiel warned. He could feel his grace being pulled out, could feel it in the way his back was arching and his wings were tugging, trying to be free. Another moment and it would burst from him, and Dean would be destroyed if he looked on it.

For once, Dean followed instructions, the sight of Castiel bowed nearly in half on the altar with his wings – and was that a halo? Yeah definitely a halo above his head.– out in the physical world spooking him enough that he knew something big was about to happen.

The moment after he managed to squeeze his eyes shut, the entire warehouse lit up with the pure blue-white electric light of a dying star. The light faded with a distinct _whoosh_ until the warehouse was back to its originally dim lighting.

Cautiously, Dean opened one eye, ready to snap it shut again if there were still bits of grace floating around. It seemed safe enough, so he opened both eyes, taking in the warehouse, now looking as if it had been power-washed, the sigils now burned into the concrete floor, and the man sitting on the altar.

Dean rushed up to him, ready to catch him if he showed the slightest signs of wooziness. Dean wasn't sure what the usual symptoms of Falling were, but he assumed they weren't pleasant. So he was startled when Castiel rose on his own, flexing his hands and rolling out his neck and shoulder muscles.

Then Cas turned, a smile lighting up his face. His blue eyes twinkled happily, and Dean knew everything was going to be okay.

"Did it work?" Dean asked, still wanting a verbal confirmation that things were okay.

"This is your problem, Dean," Castiel began cheekily, leaning in to capture Dean's lips with his own. "You have no faith." Dean laughed at that, pulling Cas closer by the belt loops and kissing him again.

When Dean finally pulled back to gasp in a breath, he exhaled a chuckle. He couldn't help the laughter, he hadn't felt this relieved and happy in a long time. "Hello, Castiel," Dean said finally with a grin.

"Hello, Dean."


End file.
